1. Field of the Invention
The field of the invention relates generally to fluid energy converters, and more particularly the invention relates to windmills and wind turbines.
2. Description of the Related Art
Fluid energy converters typically use blades, propellers, or impellers to convert kinetic energy of a moving fluid into mechanical energy, or to convert mechanical energy into kinetic energy of a moving fluid stream. For example, windmills and waterwheels convert kinetic energy from the wind or water into rotating mechanical energy, and wind turbines and water turbines further employ a generator to convert the rotating mechanical energy into electrical energy. In the reverse process, fans, propellers, compressors, and pumps can be configured to impart kinetic energy, from rotating mechanical energy, to a fluid.
Energy conversion, from kinetic to mechanical, for gases can be inefficient, especially with windmills and wind turbines. It is generally accepted that the highest efficiency possible for devices converting kinetic energy from the wind is about 59.3%. However, this number neglects losses which occur from drag and turbulence, for example. Some utility class three blade wind turbines can achieve peak efficiencies from 40-50%, while windmills are significantly lower. Therefore, there exists a need for a more efficient fluid energy converter for wind applications.
While some fluid energy converters for use with liquid fluids can achieve high efficiencies, these machines are expensive. For example, although Francis water turbines can achieve efficiencies of over 90%, they are extremely expensive. Applications exist where cost is a more important factor than efficiency maximization, and thus there exists a need for a lower cost fluid energy converter for liquid flows that still maintains a desirable efficiency.